Once Saved Always Saved versus I Corinthians 9:27

I Corinthians 9:25-27 reads “And every man that striveth for the mastery is temperate in all things. Now they do it to obtain a corruptible crown; but we an incorruptible. … But I keep under my body, and bring it into subjection: lest that by any means, when I have preached to others, I … should be a castaway.”Here Paul is saying he strives/runs to obtain an “incorruptible crown.” That’s heaven, right? (see Revelation 2:10 … and I will give thee a crown of life)But Paul goes on to say that if he didn’t keep his body under subjection, if he didn’t control the fleshly desires, he would become a “castaway.”Castaway from what? The “incorruptible crown” → heaven obviously.The Greek word translated “castaway” in I Corinthians 9:27 is translated “reprobate” 6 out of 8 times in the New Testament - II Cor 13:5, Rom 1:28, II Tim 3:8, Tit 1:16, etc. (“rejected” is the other translation).“reprobate” is defined by Random House as “rejected by God and beyond hope of salvation”So Paul (as a Christian) recognized the possibility that even he could be lost.And if it was possible for perhaps the greatest gospel preacher in history to lose his salvation, then it’s certainly possible for any Christian today to lose his/her salvation.